1. Field of the Invention
The present invention is directed to a communications device, such as, for example, a modem, and a method for enabling data communication, and in particular, to an apparatus and method that detects various communication configurations and selects an appropriate communication configuration to establish a communication link.
2. Discussion of Background and other Information
Traditionally, data communication devices, such as, for example, modems (both analog and digital), have been employed over public switched telephone networks (PSTN) to transmit data between a first location and a second location. Such modems typically operate within a conventional voice band (e.g., approximately 0 through 4 kHz bandwidth) of the PSTN. Early modems transmitted data over the PSTN at a speed of approximately 300 bit/second, or less. Over time, and with the increased popularity of the Internet, faster communication schemes (e.g., modems) were demanded and developed. Currently, the fastest analog modem available (referred to as an ITU-T V.34 modem, as defined by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T)), transmits data at a rate of approximately 33,600 bits/second under ideal conditions. Hybrid digital-analog modems, referred to as ITU-T V.90 modems, can achieve data transmission rates up to 56,000 bits/second under ideal conditions. These modems continue to exchange data within the approximate 4 kHz bandwidth of the PSTN.
It is not uncommon to transfer data files that are several megabytes (MB) in size. A modem that operates utilizing the V.34 modulation requires a long time to transfer such a file. As a result, a need has developed for even faster modems and Internet access methods.
Accordingly, many new communication methods are being proposed and/or developed to transmit high speed or broadband data on the local twisted wire pair that uses the spectrum above the traditional 4 kHz band. For example, various “flavors” (variations) of digital subscriber line (DSL) modems have been/are being developed, such as, but not limited to, for example, DSL, ADSL, VDSL, HDSL, SHDSL and SDSL (the collection of which is generally referred to as xDSL).
Each xDSL variation employs a different communication scheme, resulting in different upstream and/or downstream transfer speeds, and utilizes differing frequency bands of a twisted pair communication channel. A wide range of physical and environmental limitations of the various configurations of the twisted pair wires leads to widely varying expectations of a feasible communication capability bandwidth. Depending on, for example, the quality of the twisted wire pair (e.g., CAT3 wire vs. CAT5 wire), a given xDSL scheme may not be able to transmit data at its maximum advertised data transfer rate.
While xDSL technologies exist and offer the promise of solving the high speed data transfer problem, several obstacles exist to the rapid deployment and activation of xDSL equipment.
Several of the various xDSL schemes permit simultaneous communication on a single twisted pair in the voice band and in a frequency band above the voice band. To achieve a simultaneous voice band and above voice band communication, some xDSL variations require filters, including low pass filters, high pass filters and combinations of filters that are sometimes referred to as “splitters”. The filters separate the frequency band that carries voice band communication from the frequency band above the voice band carrying data communication. The use and type of filters may differ between installations.
Recently, there has been technology and market motivation to eliminate or reduce the use of those filters. Thus, for a given communication channel, the presence and/or type of filter is often unknown. There is a need for the communication devices to “know” the existence and configuration of such filters before initiating a communication method, as such filters impacts which communication methods are viable.
Many different xDSL and high speed access technologies solutions have been described in public, proprietary, and/or de facto standards. Equipment at each end of a connection may implement one standard (or several standards) that may (or may not) be mutually compatible. In general, startup and initialization methods of the various standards have been heretofore incompatible.
Line environments surrounding the xDSL data communication schemes, such as, for example, their ability to co-exist with a conventional analog modem that communicates within the conventional voice band (e.g., 0-4 kHz bandwidth), differences in central office equipment, the quality of the line, etc., are numerous, differ significantly, and are complicated. Accordingly, it is essential to be able to determine the capabilities of the communication channel, in addition to being able to determine the capabilities of the communication equipment, in order to establish an optimum and non-interfering communication link.
User applications can have a wide range of data bandwidth requirements. Although a user could always use the highest capacity xDSL standard contained in a multiple xDSL box, in general, that will be the most expensive service, since communication costs are generally related to the available bandwidth. When a low bandwidth application is used, the user may desire the ability to indicate a preference for a low bandwidth xDSL (and hence, a cheaper communication service), as opposed to using a high bandwidth xDSL service. As a result, it is desirable to have a system that automatically indicates user service and application requirements to the other end of the link (e.g., central office).
In addition to the physical composition of the communication equipment and communication channel, high speed data access complexity is also influenced by regulatory issues. The result has been that possible configuration combinations at each end of a communication channel have grown exponentially.
The US Telecommunication Act of 1996 has opened the vast infrastructure of metallic twisted wire pairs to both competitive (CLEC) usage, and the incumbent telephone provider (ILEC) that originally installed the wires. Thus, multiple providers may have differing responsibilities and equipment deployed for a single wire pair.
In a given central office termination, a given communication channel (line) may be solely provisioned for voiceband-only, ISDN, or one of the many new xDSL (ADSL, VDSL, HDSL, SDSL, etc.) services. Since the Carterphone court decision, telephone service users (customers) have a wide range of freedom for placing (i.e., installing and utilizing) communication customer premise equipment (e.g., telephones, answering machines, modems, etc.) on voiceband channels. However, customer premise equipment (CPE) associated with leased data circuits has typically been furnished by the service provider. As the high speed communication market continues to evolve, customers will also expect and demand freedom in selecting and providing their own CPE for high speed circuits using the band above the traditional voice band. This will place increased pressure on the service providers to be prepared for a wide range of equipment to be unexpectedly connected to a given line.
The customer premise wiring condition/configuration inside of the customer premise (e.g. home, office, etc.) and the range of devices already attached to nodes in the wiring are varied and unspecifiable. For a service provider to dispatch a technician and/or craftsman to analyze the premise wiring and/or make an installation represents a large cost. Accordingly, an efficient and inexpensive (i.e., non-human intervention) method is needed to provide for the initialization of circuits in the situation where a plethora of communication methods and configuration methods exist.
Still further, switching equipment may exist between the communication channel termination and the actual communication device. That switching equipment may function to direct a given line to a given type of communication device.
Thus, a high speed data access start-up technique (apparatus and method) that solves the various equipment, communication channel, and regulatory environment problems is urgently needed.
In the past, the ITU-T has published recommended methods for initiating data communication over voice band channels. Specifically, two Recommendations were produced:
1) Recommendation V.8 (09/94)—“Procedures for Starting Sessions of Data Transmission over the General Switched Telephone Network”; and
2) Recommendation V.8bis (08/96)—“Procedures for the Identification and Selection of Common Modes of Operation Between Data Circuit-terminating Equipments (DCEs) and Between Data Terminal Equipments (DTEs) over the General Switched Telephone Network”.
Both Recommendations use a sequence of bits transmitted from each modem to identify and negotiate mutually common (shared) operating modes, such as the modulation scheme employed, protocol, etc. However, both startup sequence Recommendations are applicable only to the conventional voice band communication methods. Further, these conventional startup sequences do not test (and/or indicate) the constitution and/or condition of the communication channel between the modems.
However, line condition information, such as, for example, frequency characteristics, noise characteristics, presence or absence of a splitter, etc., is useful at the time that plural xDSL modems are negotiating a connection, prior to actually connecting to each other, if the communications link is to be successfully established.
Voice band line probing techniques are known in the art and can be used to determine voice band line condition information. Such techniques have been used to optimize a given modulation method, such as, for example, V.34, but have not been used to optimize startup methods and/or communication selection methods. In a set of devices with multiple modulation methods, V.8 or V.8bis has been used to negotiate and then select a particular modulation. After the modulation initiation sequence has started, line probing techniques are used to receive some indication of the condition of the communication channel. If it is determined at that point that a given communication channel can not effectively support a chosen modulation method, time consuming heuristic (i.e., self-learning) fallback techniques are employed by the prior art to try and find a modulation method that works.
In order to establish an improved communication link, a method is required that observes (examines) the line conditions before attempting to select the most appropriate communication method. While techniques have been established to increase the data rate for a given modulation, the prior art does not provide a method for using channel information to aid in the selection of the communication method.
Unfortunately, in the current state of the art, capability negotiations occur without knowledge of the prevailing channel configuration. Explicit knowledge of spectrum, splitting, etc. is vital to the selection of the most appropriate communication mechanism (modulation) decision process.
Definitions
During the following discussion, the following definitions are employed:
activating station (calling station)—the DTE, DCE and other associated terminal equipment which originates an activation of an xDSL service;
answering station—the DTE, DCE and other associated terminal equipment which answers a call placed on a GSTN;
carrier set—a set of one or more frequencies associated with a PSD mask of a particular xDSL Recommendation;
CAT3—cabling and cabling componenets designed and tested to transmit cleanly to 16 MHZ of communications. Used for voice and data/LAN traffic to 10 megabits per second;
CAT5—cabling and cabling componenets designed and tested to transmit cleanly to 100 MHZ of communications;
communication method—form of communication sometimes referred to as modems, modulations, line codes, etc.;
downstream—direction of transmission from the xTU-C to the xTU-R;
errored frame—frame that contains a frame check sequence (FCS) error;
Galf—an octet having the value 8116; i.e., the ones complement of an HDLC flag;
initiating signal—signal which initiates a startup procedure;
initiating station—DTE, DCE and other associated terminal equipment which initiates a startup procedure;
invalid frame—frame that has fewer than four octets between flags, excluding transparency octets;
message—framed information conveyed via modulated transmission;
metallic local loop—communication channel 5, the metallic wires that form the local loop to the customer premise;
responding signal—signal sent in response to an initiating signal;
responding station—station that responds to initiation of a communication transaction from the remote station;
session—active communications connection, measured from beginning to end,
between computers or applications over a network;
signal—information conveyed via tone based transmission;
signaling family—group of carrier sets which are integral multiples of a given carrier spacing frequency;
splitter—combination of a high pass filter and a low pass filter designed to split a metallic local loop into two bands of operation;
telephony mode—operational mode in which voice or other audio (rather than modulated information-bearing messages) is selected as the method of communication;
transaction—sequence of messages, ending with either a positive acknowledgment [ACK(1)], a negative acknowledgment (NAK), or a time-out;
terminal—station; and
upstream: The direction of transmission from the xTU-R to the xTU-C.
Abbreviations
The following abbreviations are used throughout the detailed discussion:
ACK—Acknowledge Message;
ADSL—Asymmetric Digital Subscriber Line;
ANS—V.25 answer tone;
ANSam—V.8 modulated answer tone;
AOM—Administration, Operations, and Management;
CCITT—International Telegraph and Telephone Consultative Committee;
CDSL—Consumer Digital Subscriber Line;
CR—Capabilities Request;
CL—Capabilities List;
CLR—Capabilities List Request;
DCME—Digital Circuit Multiplexing Equipment;
DPSK—Differential encoded binary Phase Shift Keying;
DIS—Digital Identification Signal;
DMT—Discrete Multi-Tone;
DSL—Digital Subscriber Line;
EC—Echo canceling;
EOC—Embedded Operations channel;
ES—Escape Signal;
FCS—Frame Check Sequence;
FDM—Frequency Division Multiplexing;
FSK—Frequency Shift Keying;
GSTN—General Switched Telephone Network (same as PSTN);
HDSL—High level Data Link Control;
HSTU—Handshake Transceiver Unit;
IETF—Internet Engineering Task Force;
ISO—International Organization for Standardization;
ITU-T—International Telecommunication Union—Telecommunication Standardization Sector;
LSB—Least Significant Bit;
LTU—Line Termination Unit (Central office end);
MR—Mode Request;
MS—Mode Select;
MSB—Most Significant Bit;
NAK—Negative Acknowledge Message;
NTU—Network Termination Unit (Customer premise end);
OGM—Outgoing Message (recorded voice or other audio);
ONU—optical network Unit;
POTS—Plain Old Telephone Service
PSD—Power Spectral Density;
PSTN—Public Switched Telephone Network;
RADSL—Rate Adaptive DSL;
REQ—Request Message Type Message;
RFC—Request For Comment;
RTU—RADSL Terminal Unit;
SAVD—Simultaneous or Alternating Voice and Data;
SNR—Signal to Noise Ratio;
VDSL—very high speed Digital Subscriber Line;
xDSL—any of the various types of Digital Subscriber Lines (DSL);
xTU-C—central terminal unit of an xDSL; and
xTU-R—remote terminal unit of an xDSL.